The new research adds to the evidence linking specific genes to kindness and generosity, but these traits were also influenced by views about whether the world was a threatening or non-threatening place.

So although DNA may influence behavior, people do not come pre-programmed to be kind or mean or altruistic or selfish, says lead researcher Michael Poulin, PhD, of the University at Buffalo.

"We are not just puppets of our genes," Poulin tells WebMD. "Genes influence niceness in combination with perceptions of social threat, which come from our past and present experiences."

Oxytocin, Vasopressin: Niceness Genes?

Poulin and colleagues from the University at Buffalo and the University of California, Irvine, focused their research on the closely related hormones oxytocin and vasopressin, which have previously been linked to social behaviors, including love, generosity, and empathy.

They wanted to find out how expression of the two genes interacted with people's experiences and feelings to affect behavior.

To do this, they surveyed people via the Internet about their views on civic responsibility, such as whether they considered it their duty to report crimes or pay taxes, and whether they participated in charitable activities such as giving blood or attending PTA meetings.

The study participants were also asked if they viewed other people as basically "good" or "bad," and if they saw the world as more "threatening" or "non-threatening."

About 700 of those who participated also provided saliva samples for DNA analysis, which showed whether they had the specific genetic receptors for oxytocin and vasopressin that have been linked to traits associated with niceness.

People who reported finding the world to be a threatening place were generally less likely to exhibit social behaviors linked to niceness, such as charitable giving -- unless they had these versions of the genes.

The study appears in this month's issue of the journal Psychological Science.

Poulin says the fact that the genes predicted behavior only in combination with people's experiences and feelings about the world isn't surprising, because most connections between DNA and social behavior are complex.

'Love Hormone,' 'Cuddle Chemical'

Oxytocin has long been known to play a major role in childbirth and lactation, but over the last decade numerous studies have linked it more broadly to mother-child bonding and to other aspects of social interactions.

Because of this, it has variously been referred to as the "love hormone" and "cuddle chemical."

Cute names aside, University of Maryland School of Medicine professor and chair Margaret McCarthy, PhD, says the evidence that oxytocin and vasopressin play major roles in human social interaction is now quite strong.

"Humans are intensely social, and these hormones may have a lot to do with why we have evolved to be so social and so cooperative," McCarthy tells WebMD. "It is interesting that a hormone that exists for the purposes of giving birth and lactation has been co-opted to facilitate increased trust and cooperation with strangers."

She says the new research, like previous studies, highlights the interaction between genes and environment in determining behavior.